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[Karol Brzezinski <question703169@xxxxxxxxxxxxxxxxxxxxx>]

Question #703169 on Yade changed:
https://answers.launchpad.net/yade/+question/703169

Karol Brzezinski posted a new comment:
Hi Xu,

Thank you for your MWE. It looks like it is not what I thought at the beginning. I don't know what is the reason. 
My last clue is that 'utils.getStress()' may give slightly different results for clumps and spheres. I modified oedometric test example [1] to check this. But the results for different simulations are scattered.
################################################
from yade import pack, plot

useClumps = True

readParamsFromTable(rMean=.075, rRelFuzz=.3, maxLoad=1e6)

from yade.params.table import *

# create box with free top, and ceate loose packing inside the box
O.bodies.append(geom.facetBox((.5, .5, 1), (.5, .5, 1), wallMask=31))
sp = pack.SpherePack()
sp.makeCloud((0, 0, 0), (1, 1, 2), rMean=rMean, rRelFuzz=rRelFuzz)
sp.toSimulation()
# make material frictionless to avoid force acting on vert walls
O.materials[0].frictionAngle = 0   

# I just make spheres smaller to avoid overlapping after replacing by clumps
for b in O.bodies:
	if isinstance(b.shape, Sphere):
		b.shape.radius*=0.8

if useClumps:
	
	relRadList2 = [1,1]
	relPosList2 = [[0.5,0,0],[-0.5,0,0]]
	templates= []
	templates.append(clumpTemplate(relRadii=relRadList2,relPositions=relPosList2))
	O.bodies.replaceByClumps(templates,[1.],discretization=10)
	
O.engines = [
        ForceResetter(),
        InsertionSortCollider([Bo1_Sphere_Aabb(), Bo1_Facet_Aabb(), Bo1_Wall_Aabb()]),
        InteractionLoop(
                [Ig2_Sphere_Sphere_ScGeom(), Ig2_Facet_Sphere_ScGeom(), Ig2_Wall_Sphere_ScGeom()],
                [Ip2_FrictMat_FrictMat_FrictPhys()],
                [Law2_ScGeom_FrictPhys_CundallStrack()]
        ),
        NewtonIntegrator(gravity=(0, 0, 0), damping=0.1),
        PyRunner(command='checkUnbalanced()', virtPeriod=1, label='checker'),
]
O.dt = .5 * PWaveTimeStep()

def checkUnbalanced():
	# at the very start, unbalanced force can be low as there is only few contacts, but it does not mean the packing is stable
	if O.iter < 5000:
		return
	# the rest will be run only if unbalanced is < .1 (stabilized packing)
	if unbalancedForce() > .1:
		return
	# add plate at the position on the top of the packing
	# the maximum finds the z-coordinate of the top of the topmost particle
	O.bodies.append(wall(max([b.state.pos[2] + b.shape.radius for b in O.bodies if isinstance(b.shape, Sphere)]), axis=2, sense=-1))
	global plate  # without this line, the plate variable would only exist inside this function
	plate = O.bodies[-1]  # the last particles is the plate
	# Wall objects are "fixed" by default, i.e. not subject to forces
	# prescribing a velocity will therefore make it move at constant velocity (downwards)
	plate.state.vel = (0, 0, -.01)
	# start plotting the data now, it was not interesting before
	O.engines = O.engines + [PyRunner(command='addPlotData()', iterPeriod=200)]
	# next time, do not call this function anymore, but the next one (unloadPlate) instead
	checker.command = 'unloadPlate()'


def unloadPlate():
	# if the force on plate exceeds maximum load, start unloading
	if abs(O.forces.f(plate.id)[2]) > maxLoad:
		plate.state.vel *= -1
		O.pause()
		print('Stress underestimated by the factor {:.2f}'.format(max(plot.data['Fz'])/max(plot.data['szz'])))


def addPlotData():
	if not isinstance(O.bodies[-1].shape, Wall):
		plot.addData()
		return
	Fz = O.forces.f(plate.id)[2]
	szz=-1*utils.getStress()[2,2]
	plot.addData(Fz=Fz,szz=szz, w=plate.state.pos[2] - plate.state.refPos[2], unbalanced=unbalancedForce(), i=O.iter)


# besides unbalanced force evolution, also plot the displacement-force diagram
plot.plots = {'w': ('Fz','szz')}
plot.plot()

O.run()


################################################
Best wishes,
Karol

[1] https://yade-dem.org/doc/tutorial-examples.html#oedometric-test

PS Jan, sorry for suggesting this 'interaction inside clump' issue, but
I can swear I encountered this some time ago.

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